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19204Re: [rest-discuss] URI design, part 2

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  • Max Toro
    Dec 1, 2012
      Thanks for you answer Erik. I don't want to repeat myself, so please
      see my answer to Eric, I'd love to get your comments as well. Rather
      than good or bad I'd like to determine if my example is REST or not.
      Max Toro

      On Sat, Dec 1, 2012 at 10:30 AM, Erik Mogensen <erik@...> wrote:
      > This post is mostly aimed at Max Toro, but Eric provided a nice entry point
      > for me :-)
      > On Sat, Dec 1, 2012 at 8:08 AM, Eric J. Bowman <eric@...>
      > wrote:
      >> Max Toro wrote:
      >> >
      >> > What I'd love to get is an answer like: POST /orders/1/cancel is not
      >> > REST compliant because chapter x of Fielding's dissertation explicitly
      >> > or implicitly says it's not allowed or it's discouraged.
      >> >
      >> Well, what are you expecting to GET from /cancel, or are you just using
      >> that URL to invoke a procedure? [...]
      >> Suggested reading: 6.5.2; 6.2.1, in particular:
      >> "REST [defines] a resource to be the semantics of what the author
      >> intends to identify."
      > Exactly. And we don't know what the author intends to identify just by
      > looking at the path /orders/1/cancel.
      > Just looking at the syntax of a single request (e.g. the method POST and/or
      > the path /orders/1/cancel) is not enough to determine if the system adheres
      > to any particular architectural style.
      > The author may well intend that /cancel identifies a resource, and allow
      > lots of interaction in it. It might even have an HTML representation, with
      > a nice <form method="post"><input type="submit" value="CANCEL"></form> in
      > it.
      > But this is still not enough to determine if a system adheres to the
      > constraints: For even though the server provides such hypermedia controls,
      > media types and does everything "by the book", it is still up to the
      > *client* to actually *use* these hypermedia controls. In fact it is up to
      > the author of the agent itself.
      > If you write code in the client that hard wires a button called "cancel" to
      > the "POST /orders/1/cancel" HTTP request then the client isn't really
      > honouring the hypermedia controls laid out above. If, however, it _soft
      > wires_ the same button _because_ of the hypermedia control above, then
      > you're doing it "more right" I would say. The point is that the client
      > should be written in such a way that it uses _only_ the hypermedia controls
      > that it receives at run-time.
      >> Roy's thesis really must be considered in its entirety, [...]
      > +1 to such a degree that 1 > 1. The rest of the stuff you wrote was great.
      > I just want to highlight the incorrectness of the question, as others said
      > earlier that REST doesn't say anything about if POST /foo is or isn't...
      > For all we know /orders/1/cancel is a picture of a dog, or it could be a
      > SOAP endpoint for a nice game of Global Thermonuclear War.
      > The constraints of REST are too often thought / taught to deal with the
      > server side, but in my experience, it has much more to do with the client
      > side, how much knowledge the client has on things like:
      > - what URLs can it use? (it shouldn't know any; but bind to one at run-time,
      > preferably via a configuration parameter)
      > - when it knows one URL (e.g. "/orders/1"), can it add "/cancel" to it to
      > cancel it? (no, unless it was told to add "/cancel" by a hypermedia
      > control)
      > - does it know the "type" of a resource, e.g. that /orders/1 is an Order
      > (this is a point of contention on the list; browsers don't know about books
      > or a bank account, but work fine nonetheless.)
      > - when it does know the type of the URL is an order, does it pull up a
      > pre-coded "order" UI (bad), or does it create a UI based on what it finds in
      > the response (good)
      > --
      > -mogsie-
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